1. Field of the Invention
The present invention relates to a component-embedded circuit substrate with capacitors embedded therein.
2. Description of Related Art
Capacitors, which are single electronic components, have differing frequency characteristics due to a variety of factors such as the dielectric type, capacitance, and size of each capacitor. Therefore, when using a capacitor in an electronic device, it is difficult to achieve desired characteristics with only a single capacitor. As a countermeasure, it is common to mount a plurality of capacitors in parallel, with each having a different frequency. A typical mounting example of this includes the so-called bypass capacitor (or decoupling capacitor). The bypass capacitor is arranged between the power line and ground in order to stabilize the operation of the electronic circuits. The bypass capacitor lowers the alternating current impedance of the power line with respect to ground and also functions as a filter to eliminate noise. In practice, a capacitor that has a large capacitance but poor high frequency band characteristics is connected in parallel with a capacitor that has a significantly smaller capacitance but good high frequency band characteristics and these are used as the bypass capacitor.
In the manufacturing process of the electronic device, an inspection is performed after the electronic components are mounted on the circuit substrate in order to find mounting defects such as soldering defects or wiring disconnection. However, with parallel capacitor circuits such as bypass capacitors, there are instances when a proper inspection is not possible by merely measuring the composite capacitance. In other words, when the capacitance of one capacitor is less than or equal to the capacitance tolerance range of another capacitor, the value of the measured composite capacitance is in the tolerance range of the capacitor with the larger capacitance even if there is a mounting defect with the capacitor having the smaller capacitance. Thus, the connection defect cannot be detected.
Known methods of inspection to solve this type of problem are respectively disclosed in Patent Documents 1 and 2. In the method disclosed in Patent Document 1, spike voltage waveforms set to the respective frequency bands of the large capacitance capacitor C1 and small capacitance capacitor C2 are used to inspect these capacitors. In the method disclosed in Patent Document 2, a signal generating source is used to generate a prescribed voltage, which is inputted to the output terminal of the capacitor by a probe 1, and measurement is performed by probes P2 and P3 (link guard) connected to the input terminal side of the capacitor.